Epigenetic alterations in neuroendocrine tumors: methylation of RAS-association domain family 1, isoform A and p16 genes are associated with metastasis.

Well-differentiated neuroendocrine tumors including pancreatic endocrine tumors and carcinoid tumors are uncommon neoplasms that have site-specific differences in clinicopathological features, clinical course and genetic alterations. The epigenetic alterations in these tumors are not well characterized. We therefore compared methylation of the RAS-association domain family 1, isoform A (RASSF1A), p14, p16 and O6-methyl-guanine methyltransferase genes in neuroendocrine tumors from 47 patients including 16 pancreatic, 15 nonileal and 16 ileal neuroendocrine tumors. Methylation of the RASSF1A gene was present in 57% of tumors, p14 in 49%, p16 in 26% and O6-methyl-guanine methyltransferase in 13% of tumors. Ileal neuroendocrine tumors lacked methylation of O6-methyl-guanine methyltransferase gene (P = 0.04). RASSF1A methylation was associated with histopathologic type of tumors (P = 0.03) and lymph node metastasis (P = 0.004), and p16 methylation with older patient age (P = 0.002) and liver metastasis (P = 0.04). Two or more genes were methylated in 53% of tumors, one gene was methylated in 30% of tumors, and all four genes were unmethylated in 17% of tumors. Methylation of one or more gene was associated with older age of patients (P = 0.01), and methylation of two or more genes was associated with liver metastasis (P = 0.044). Our study shows that in neuroendocrine tumors epigenetic alterations vary by tumor subsite and clinicopathologic features, including age of onset, histopathologic type and metastasis status.